The present invention relates to a refractory shutoff assembly for use in controlling, regulating and interrupting the discharge of molten metal from a metallurgical vessel. More particularly, the present invention relates to such a refractory shutoff assembly including a refractory inner pipe or stator to be fixedly mounted in a bottom of the metallurgical vessel, such inner pipe having therethrough at least one transverse opening at a position to be above the vessel bottom when the inner pipe is fixedly mounted therein. The assembly further includes a refractory outer pipe or rotor to be mounted about the inner pipe, the outer pipe having therethrough at least one transverse opening, and the outer pipe having a lower end. The outer pipe is movable relative to the inner pipe axially thereof between an open position, whereat the at least one opening in the outer pipe aligns with the at least one opening in the inner pipe, and a closed position whereat the at least one opening in the inner pipe is isolated from the at least one opening in the outer pipe. The outer pipe also may be rotatably movable relative to the inner pipe to move the outer pipe between open and closed positions.
Such a refractory shutoff assembly is disclosed in German DE 35 40 202. In such reference, to control the discharge of molten metal, an outer pipe can be rotated and moved axially relative to a fixed inner pipe. When the outer pipe is in a closed position, the openings through the two pipes are out of alignment so that molten metal discharge is interrupted.
However, such known arrangement suffers from an inherent disadvantage. Particularly, when the outer pipe is displaced axially by its maximum closing stroke relative to the inner pipe to a closed position, there remains a space between the lower end of the outer pipe and the bottom of the vessel. In such space the outer surface of the inner pipe is totally exposed to the molten metal within the metallurgical vessel. Thus, any cracks that may exist in the inner pipe are not covered by the outer pipe. Accordingly, a molten metal break through such cracks is possible. Additionally, in operation of such known device, in the event of a maximum displacement of the outer pipe in the axial direction to a closed position, the outer pipe makes contact with the upper end of the inner pipe that is positioned within the outer pipe. As a result, the upper end of the inner pipe is subjected to mechanical stresses which increases the likelihood of formation of cracks in the inner pipe and thereby the risk of molten metal breakthrough. Consequently, the refractory shutoff assembly disclosed in such German reference does not provide for operationally adequate emergency closing of the assembly.